Landline calls drop on All Phones

Very frustrating. It usually is on longer calls, but many drop anywhere from 5-15 minutes and I get a busy signal. Been on some important calls and some where I was dealing with support issues on turbo tax and lately an important one doing financial transactions with my planner. Very frustrating. It's happened on all my phones, even the one plugged into my modem. I see from googling this subject, that this is quite common. When I went into My Account App, it asked me to reset my modem. I did this, but my modem has been reset already many times remotely from Comcast tech support for other issues. Anyhow, I really don't think I should have to pay for phone service if Comcast can not provide reliable service.